1. Field of the Invention
This invention relates generally to the field of dentistry and more particularly to endodontic instruments used for cleaning and enlarging a root canal of a tooth.
2. Description of the Related Art
Instruments that enable an endodontist to clear and clean the canal of a tooth are well-known in the art. These instruments, typically referred to as endodontic files, experience significant flexing and twisting while in use, making them susceptible to breakage. Because of the breakage problem and the danger that it poses to a patient, nickel-titanium alloy (NiTi or Nitinol™) generally is viewed as a better material for use in manufacturing these instruments than is stainless steel. Relative to stainless steel, NiTi is able to withstand a far greater amount of twisting or bending without experiencing permanent deformation or breaking.
The manufacturing methods typically used for producing stainless steel instruments have proven themselves unsatisfactory when applied to NiTi. These methods include (1) twisting a prismatic rod having a square or triangular cross section to create a file with a fluted cutting edge and (2) grinding helical flutes along the length of a circular or tapered rod to create a file with one or more helical cutting surfaces. Twisting cannot be used because of the superelastic property of NiTi and traditional grinding methods leave areas of stress having radial planar components that reduce the torsional resistance of a file.
Methods of manufacturing specifically designed for NiTi provide a clean cutting edge but involve grinding or hacking methods that reduce the torsional strength of the file by creating stress areas lying perpendicular to the longitudinal axis of the file. The same is true of the traditional grinding and hacking methods used to form a file made of stainless steel. Breakage of the file due to torsion usually occurs in one or more of these cross-sectional areas. Additionally, currently available methods of grinding NiTi for use as an endodontic file are relatively expensive and slow. Therefore, a need exists for a method of manufacturing an endodontic file made of stainless steel or NiTi—or other materials that exhibit the desired superelastic properties of NiTi—that does not erode the torsional strength of the file. None of the prior art alone or in combination meets this need or renders the present invention obvious.
For background information relating to instruments of the type that is the subject of this patent application, reference may be had to the following issued United States patents and publications:
U.S. Pat. No.InventorTitle4,871,312HeathDental Compactor Instrument4,934,934Arpaio, Jr. et al.Dental File/Reamer Instrument5,035,617McSpaddenEndodontic Instrument5,065,549Speiser et al.Method and Apparatus For Manufacturing K-Files and Reamers5,184,926HemmingsRoot-Strength Drill Bit and Method of Making5,628,674Heath et al.Endodontic Instrument5,653,590Heath et al.Kit of Endodontic Instruments and Method of Utilizing Same5,735,689McSpaddenEndodontic Dental Instrument5,735,690MalentaccaSet of Drills For The Boring Of The Coronary Part of DentalRadicular Canals6,149,501Farzin-Nia et al.Superelastic Endodontic Instrument, Method of Manufacture, andApparatus Therefor6,299,445GarmanEndodontic Instrument, Instrument Blank and Method ofManufacture7,018,143MooreReduced Energy Consuming, Lateral Cutting Twist Drill7,018,205AbelBarbed Endodontic Instrument2004/0,219,484ScianambloEndodontic Instrument Having Reversed Helix2006/0,014,480Aloise et al.Method of Manufacturing A Dental Instrument2006/0,265,858McSpaddenEndodontic Instrument Having Notched Cutting Surfaces